Reclamation is the process of reclaiming unused space on a tape (applies to Virtual Tapes as well). Over time the TSM expiration process will expire old data, creating gaps of unused storage on the tapes.  Because Tapes are sequential media, TSM can only write data to the end of the tape, so these gaps of “Empty Space” cannot be used.

Lets see an illustration of this

Tape 1 is a new tape and data is written to it as follows (each number on the following line represents a file being backed up)

1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16

Over time the expiration runs and expires old files (The * represents an expired file)

1-2-3-*-5-*-*-8-9-*-*-*-13-14-15-16

TSM refers to this space ‘*’ as Reclaimable Space.

TSM can only write to the end of the tape and the Reclaimable Space cannot be reused until all the data on the tapes expires and the tape becomes a scratch tape again.

To view this reclaimable space

QUERY VOLUME volno F=D   (where volno is the Volume Number for the Tape ) and look at the Pct Reclaimable Space field.

When using TSM Studio open the Volumes dataview from the Libraries and Volumes Category and view the Pct Reclaim Column

To get back this reclaimable space TSM has a Reclamation process which copies all the valid information from the tape to a new scratch tape so looking at our previous illustration TSM will create the new tape with the valid files

1-2-3-5-8-9-13-14-15-16

This eliminates all the reclaimable space and the old tape becomes a scratch tape.

On each Storage Pool supporting reclamation there is a Reclaim Threshold parameter

Run the QUERY STGPOOL stgpoolname F=D and look at the Reclamation Threshold field

Or when using TSM Studio, open the Storage Pools dataview in the Storage Category and check the Reclaim column

NOTE:  For tapes with a value of READWRITE or READONLY in the ACCESS column. TSM will run the reclamation on them when they are FULL, if they are FILLING they will not be touched.

Tapes in an OFFSITE status in a copy pool will be reclaimed whether or not they are FILLING or FULL.

To Change the Reclamation Threshold for a Storage Pool use the following command

UPDATE STGPOOL stgpoolname RECLAIM=xx  ( stgpoolname is the storage pool and RECLAIM is the threshold to use )

On TSM Studio right click on the Storage Pool and select Reclamation Threshold and either choose one of the values or use the SET option to choose another value.

As there are a number of admin jobs and backup jobs that all need to use tape drives, you will need to find the right window to run your reclamation processes and decide how many processes you wish to run. Remember that each process will require 2 tapes drives, one for the input tape and one for the output tape. Automatically starting and stopping your reclamation processes can be done with Administration Schedules. ( Check back soon to see an article on Admin Schedules )

Posted in: TSM Studio